Digital radio for carrier telephony appeared in the early 1970's and was limited to modest spectral efficiencies and relatively short distances. The field has grown greatly over the past decades and the use of digital radios is widespread. Consequently, networks and protocols for more efficiently scheduling, facilitating and synchronizing communication over digital radio transmission systems have also increased.
One family of protocols employed in digital communications systems are Carrier Sense Multiple Access (CSMA) protocols. CSMA protocols generally can be considered as methods for distributing management of a communication medium among users of the medium. The medium within which CSMA protocols are concerned is a single carrier communication medium, such as a transmission channel in a digital radio voice/data network. Although many variants of CSMA protocols are known, many CSMA protocols employ a scheme whereby each node sharing the communication medium is assigned a random time slot during which the node may initiate transmission provided no other node has already begun a transmission. The set of time slots for all nodes is synchronized to within one propagation time interval with the trailing edge of a carrier signal that follows the end of a transmission on the communications medium. Under this scheme, nodes on the network must maintain strict transmission and reception time interval requirements in order to effectively communicate via the network.
Although voice/data packet networks employing CSMA principles are used in digital radio communications systems, such communications have been problematic. For instance, communications become difficult once a radio is out of range or out of the line of sight. Although a radio receiver may be in range to receive a communication from a radio transmitter, it cannot receive a signal through a barrier (e.g., a mountain) from a transmitter located on the other side of the barrier. In order for the radio transmitter to communicate with the receiver, a repeater or retransmitter located at the barrier must be used to receive the transmitted signal and then retransmit the information to the receiver.
Currently, a retransmit receiver radio processes received data from the transmitter radio after receiving a synchronization sequence and sends the data as an asynchronous stream over a retransmit interface to a retransmit transmitter. During this time interval, the retransmit transmitter must wait before it transmits a synchronization sequence to the radio receiver, along with the asynchronous data stream. This method proves problematic in a voice/data packet network employing a CSMA contention interval with slots of time to manage network access. The retransmitter incurs an intolerable amount of delay when considering the CSMA contention interval. This delay disturbs the CSMA contention interval and causes the radio transmitter and radio receiver to be out of CSMA synchronization with each other because the delay causes the retransmitter to have a small probability of capturing the network within the appropriate time interval. This degrades the performance across the network and ultimately prevents communication between the transmitter and receiver. Consequently, it is extremely desirable to have an improved system for retransmitting digital radio signals within a CSMA network in such a way as to maintain synchronization on both sides of the retransmitter in order to facilitate voice/data communications.